Summary:
Adds a new Record Card view section to each non-summary table, which can be from opened from various parts of the Grist UI to view and edit records in a popup card view.
Work is still ongoing, so the feature is locked away behind a flag; follow-up work is planned to finish up the implementation and add end-to-end tests.
Test Plan: Python and server tests. Browser tests will be included in a follow-up.
Reviewers: jarek, paulfitz
Reviewed By: jarek
Subscribers: paulfitz
Differential Revision: https://phab.getgrist.com/D4114
